This invention relates to automatic power transmissions in general, and especially to automatic bicycle power transmissions.
Bicycles have employed chain and sprocket type transmissions for many years now. Typically, they include an array of sprockets mounted on both driver and driven shafts. These sprockets offer the rider a selectable choice of drive ratios thereby allowing the rider to taylor the drive to his or her own level of comfort or ability. The chain which transfers power from the driver to the driven shaft is shifted by means of a "derailleur" mechanism which moves the chain laterally from sprocket to sprocket. Although this drive system is highly efficient, light weight, cost effective and simple, it nevertheless possesses a number of tangible shortcomings and disadvantages.
One such disadvantage, for example, is the relative complexity of the derailleur type transmission. Each lateral movement of the chain from one sprocket to another requires a corresponding compensation in the length of the chain. This unfortunately necessitates the use of a self-adjusting type tensioner which adds further complexity to the design. Moreover, any slight misalignment of the cable driven front and rear derailleur mechanisms can create an inefficient "between gears" condition.
Another disadvantage of the derailleur type transmission is that when undergoing a sprocket change, the lateral movement of the chain creates a discontinuity in the power transmission to the rear wheel which results in a loss of propulsive force.
Still another disadvantage is the difficulty of bringing the bicycle up to speed upon acceleration from a stand-still position where the rider happens to be in a high gear mode instead of a low gear mode. In such cases, the bicycle must be in forward motion to effect a gear change to a lower gear, which is of course after the fact.
A further disadvantage is that the rider must constantly make manual gear changes to compensate for variable loading conditions resulting from external factors including, but not limited to, road inclination, tire pressure and windage, for example.
A still further disadvantage of the derailleur type transmission is simply that many people find it difficult to understand how the gears operate and therefore avoid these bicycles altogether.
It is therefore an important object of the invention to provide an improved automatic transmission system.
Another object of the invention is to provide an improved automatic transmission system which is an alternative for the present day bicycle derailleur type transmissions.
Another object of the invention is to provide a self-regulating and automatic bicycle transmission which is simple in design and operation.
Still another object of the invention is to provide such an automatic bicycle transmission while maintaining high levels of power efficiency.
A further object of the invention is to provide such an automatic bicycle transmission which is light-weight, economical and inexpensive to manufacture.